福島県環境創造センター
Fukushima Environmant Creation Center

Aging management of concrete structures in existing nuclear power plants with respect to the alkali–silica reaction (ASR) is a challenge in Japan. The Nuclear Regulation Authority (NRA) has been organizing a project on advanced integrity evaluation technology for aging management of structures. In this paper, the activities of a working group studying the ASR are introduced. ASR management does not only mean identification or diagnosis of ASR but also includes performance evaluation of structures in order to judge whether the structure can maintain its performance during a required period. The NRA has a pivotal role in evaluating applications provided by utility companies for aging management of nuclear power plants (NPP). However, in Japan, the available countermeasures for ASRs are intended for general civil structures and architectural buildings, and there is insufficient experience and data related to evaluation systems for NPPs, which require high-level safety and multifunctions, such as shielding performance, pipe and cable supporting performance, and seismic performance. In particular, regarding slow-reactive aggregates, which have been under focus recently, quantitative data are scarce and evaluation methods and countermeasures have not been established. Therefore, in the current project, before discussing aging management, the alkali reactivity of typical Japanese reactive aggregates are first evaluated using various Japanese and international test methods and a reasonable procedure for evaluating the alkali reactivity of aggregate or concrete mixtures is investigated. Next, methods for ASR diagnosis are verified. Simultaneously, concrete expansion estimation and performance evaluation within the scope of aging management are discussed, and target research topics are outlined for establishing an effective evaluation system for NPP concrete structures at risk of ASR-induced damage.